Are there differences between the various strains of Human Parainfluenza Virus (HPIV)?

From the Guidelines

Yes, there are significant differences between the different strains of parainfluenza viruses, with types 1 and 2 most commonly associated with croup syndrome, and type 3 associated with bronchiolitis and pneumonia. The different strains of parainfluenza viruses have distinct epidemiological and clinical characteristics, as outlined in a 2018 update by the Infectious Diseases Society of America and the American Society for Microbiology 1.

Key Differences Between Strains

• HPIV-1 and HPIV-2 are most commonly associated with croup syndrome
• HPIV-3 is associated with bronchiolitis and pneumonia, particularly in infants and young children
• The strains differ in their seasonality, with HPIV-1 and HPIV-2 typically appearing in fall and winter, and HPIV-3 circulating year-round with peaks in spring and summer

Diagnostic Approaches

• Respiratory secretions or nasopharyngeal swabs are the specimens of choice for diagnosis
• Diagnostic tests include culture and nucleic acid amplification tests (NAATs), which are now common in commercial respiratory panels 1

Clinical Implications

• Understanding the differences between the strains is important for diagnosis, treatment approaches, and understanding outbreak patterns in different populations
• Parainfluenza virus infections account for up to 11% of all hospitalizations in children <5 years old, highlighting the need for accurate diagnosis and effective treatment strategies 1

From the Research

Differences between Parainfluenza Strains

• There are four serotypes of human parainfluenza viruses (HPIVs) that cause respiratory illnesses in children and adults 2.
• Each serotype has different characteristics, such as the ability to cause certain types of illnesses, like otitis media, pharyngitis, conjunctivitis, croup, tracheobronchitis, and pneumonia 2.
• The clinical manifestations of parainfluenza virus infections can range from mild illness to severe croup, bronchiolitis, and pneumonia, depending on the serotype and the host's immune status 3.

Viral Entry Requirements

• The molecular determinants for HPIV3 growth in vitro are fundamentally different from those required in vivo, and these differences impact inhibitor susceptibility 4.
• Clinically circulating viruses have fusion machinery that is more stable and less readily activated than viruses adapted to growth in culture 4.
• The unique susceptibility of clinical strains in human tissues reflects viral inhibition in vivo, and antivirals should be evaluated using clinical isolates in natural host tissue rather than lab strains of virus in cultured cells 4.

Treatment and Prevention

• There are no effective antiviral therapies available for parainfluenza virus infections, and treatment is primarily supportive 2.
• A multi-drug regimen including inhaled ribavirin, corticosteroids, and intravenous immunoglobulin (IVIG) has been shown to be safe and effective in treating RSV and PIV infections in adult lung and heart-lung transplant recipients 5.
• Continuous global viral surveillance is essential to monitor antigenic changes that may occur in nature, particularly with regards to the implementation of diagnostic assays 6.

Antigenic Variation

• Naturally occurring parainfluenza virus type 2 (hPIV-2) variants have been characterized, and these variants exhibit unusual phenotypic and antigenic characteristics 6.
• The differences observed in the fusion (F) and hemagglutinin-neuraminidase (HN) genes between the prototype strain and clinical hPIV-2 variants could explain their antigenic variation and provide new data for the analysis of Paramyxovirus fusion mechanisms and their pathogenesis 6.